(1) Field of the Invention
The present invention relates to solid-state imaging devices and methods for fabricating the devices, and particularly relates to a sensitive solid-state imaging device including color separators with high light transmittance and a method for fabricating the device.
(2) Background Art
Solid-state imaging devices such as CCD solid-state imaging devices and MOS solid-state imaging devices are used for various image input equipment such as video cameras, digital still cameras and facsimiles.
In a solid-state imaging device, a microlens is generally provided on a chip in order to increase the amount of light incident on light-receiving parts for performing photoelectric conversion (see, for example, Japanese Unexamined Patent Publication No. 64-10666). A microlens is, for example, a layer made of an inorganic or organic transparent material and processed into a convex shape and focuses light by refracting incident light at the convex surface. However, in a conventional solid-state imaging device including color filters, only one-third of focused light enters light-receiving parts.
To obtain a color image in a solid-state imaging device, it is necessary to decompose focused light into color components and then make the respective color components enter light-receiving parts. Color components are generally separated by using absorption color filters (color separators) respectively associated with three colors of red (R), green (G) and blue (B). A green absorption filter, for example, absorbs red light and blue light and transmits only green light. Accordingly, when light passes through the absorption color filter, two-thirds of the light is absorbed. As a result, light incident on light-receiving parts is reduced to one-third of focused light, so that the sensitivity of the solid-state imaging device decreases.
On the other hand, transmission color filters are used in, for example, display apparatus. The transmission color filters are formed in combination with dichroic mirrors each of which transmits light with a specific wavelength and reflects light with the other wavelengths (see, for example, Japanese Unexamined Patent Publication No. 8-54623). Accordingly, in the case of using transmission color filters in a solid-state imaging device, if a dichroic mirror which transmits only green light, for example, is used to separate green light and make the green light enter a light-receiving part and reflected light from which the green light has been separated is further separated and caused to enter other light-receiving parts, light incident on the solid-state imaging device is used without waste.
However, when the conventional transmission color filters are used in a solid-state imaging device, the following problems arise. The solid-state imaging device uses color filters in a Bayer pattern in which adjacent four light-receiving parts arranged in two rows and two columns are generally used as a set so that green light enters two of the light-receiving parts and red light and blue light enter the other two light-receiving parts. This is because human vision has higher sensitivity to green light and, therefore, the number of light-receiving parts which receive green light is increased so as to enhance the resolution of an image. However, the conventional transmission color filters separate incident light into three light beams of red, green and blue. Accordingly, light-receiving parts which receive red light, green light and blue light, respectively, are arranged in a line, thus making it difficult to arrange color filters in a Bayer pattern.